You must at least have a Dubsado Trial account to have an affiliate code.
 

How do I get a code?

Login to Dubsado and click your logo at the top right
Then click AFFILIATE
Lastly, make your code!

What do coupon codes do? 
For each person that signs up using your code...

YOU GET: A month free in credits.
THEY GET: 20% off their first month or year.